Spectroscopic studies of photobleaching and photoproduct formation of meta(tetrahydroxyphenyl) chlorin (m-THPC) used in photodynamic therapy. The production of singlet oxygen by m-THPC
C. Hadjur et al., Spectroscopic studies of photobleaching and photoproduct formation of meta(tetrahydroxyphenyl) chlorin (m-THPC) used in photodynamic therapy. The production of singlet oxygen by m-THPC, J PHOTOCH B, 45(2-3), 1998, pp. 170-178
Citations number
40
Categorie Soggetti
Biochemistry & Biophysics
Journal title
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY
Meta(tetrahydroxyphenyl)chlorin (m-THPC) is a new photosensitizer currently
undergoing clinical trials at Lausanne's CHUV hospital for photodynamic th
erapy (PDT) of early cancer in the upper aerodigestive tract. The illuminat
ion of m-THPC with light at 650 nn in aqueous solution containing 10% foeta
l calf serum (FCS) causes two simultaneously occurring processes: its photo
degradation and the formation of a more stable photoproduct absorbing at 32
0 mn. The photodegradation quantum yield (Phi(Pb)) of m-THPC is found to be
of the order of 1.5 x 10(-5) in 10% FCS. A strong dependence on oxygen con
centration of the photodegradation and the formation of photoproducts has b
een observed. Indeed, the m-THPC presents rather low Phi(Pb) under Nz-satur
ated conditions: 6.9 x 10(-6). In aerobic conditions, the photodegradation
as well as the formation of photoproducts, have been competitively inhibite
d by known singlet oxygen (O-1(2)) quenchers. The addition of superoxide di
smutase (SOD), catalase or desferal, known quenching agents of type I mecha
nisms, has little or no effect on the rate of photobleaching and photoprodu
ct formation of m-THPC. m-THPC generates O-1(2) With a quantum yield of 0.3
in ethanol solution as determined by photo-oxidation experiments using 1,3
-diphenylisobenzofuran (DPBF) as substrate. The rate and quantum yield of D
PBF photo-oxidation are found to increase with increasing substrate concent
ration and decrease in phosphate buffer solution (Phi(Delta) = 0.01), due t
o the partially hydrophilic character of m-THPC. In addition, the reaction
of O-1(2) with TEMP (2,2,6,6-tetramethyl-4-piperidone) in combination with
electron paramagnetic resonance (EPR) detection has been used to determine
the formation of O-1(2) by m-THPC in ethanol solution. (C) 1998 Elsevier Sc
ience S.A. All rights reserved.